A present invention is related to an improved locating structure for a silicon sheet of a motor locator. The locating structure is able to truly locate the silicon sheet and aim the silicon sheet at a chip sensing point of a sensing switch.
FIGS. 4 and 5 show a conventional wiperless DC motor. The motor includes a base board 81 formed with a central fixing hole 82. A bush 86 of a locator 85 is fixedly fitted in the fixing hole 82. A silicon sheet 84 is inlaid in each of the top and bottom faces of the locator 85. Each silicon sheet 84 has several pole sections 841. The locator 85 has several downward extending fixing rods 851. The base board 81 has a sensing switch 83 having a chip sensing point 831. The base board 81 has several fixing holes 811 respectively corresponding to the fixing rods 851. The fixing rods 851 are inserted in the fixing holes 811 for locating the locator 85. When located, the edge of one of the pole sections 841 of the silicon sheet 84 is aimed at the chip sensing point 831 of the sensing switch 83. The shaft 871 of a rotor 87 is disposed in the bush 86 of the locator 85. The rotor 87 has an annular permanent magnet 88 fitted around the locator 85. The coil in the locator 85 is controlled by the sensing switch 83 to create magnetic force of different polarities at the pole sections 841 of the silicon sheet 84. Accordingly, the permanent magnet 88 is driven to rotate the rotor 87 for driving a fan (not shown).
In the above structure, the fixing rods 851 are integrally formed in integral injection molding of the locator 85. The cross-section of the fixing rod 851 has small area so that when demolded, the fixing rods 851 tend to bend and deform. As a result, when using the fixing rods 851 to fix the locator 85, the fixing rods 851 are often deflected so that the pole sections 841 of the silicon sheet 84 can be hardly accurately aimed at the chip sensing point 831 of the sensing switch 83. In more serious case, the rotor 87 may be unable to rotate.
Moreover, the fixing rods 851 are integrally formed with the locator 85. Therefore, when the fixing rods 851 are inserted in the fixing holes 811, it is the locator 85 which is directly located, not the silicon sheet 84. In other words, the silicon sheet 84 is indirectly located by the fixing rods 851. Such locating measure tends to cause error of position where the silicon sheet 84 is inlaid in the locator 85. As a result, the silicon sheet 84 can be hardly truly located. In serious case, the rotor 87 may be also unable to rotate.
The sensing switch 83 through the chip sensing point 831 senses the variation of magnetic force of the pole sections 841 of the silicon sheet 84 so as to control turning on/off of the coil in the locator 85. Accordingly, the pole sections 841 of the silicon sheet 84 can create magnetic force of different polarities to drive the rotor 87 for driving the fan. Therefore, it is critical to accurately aim the pole sections of the silicon sheet at the chip sensing point of the sensing switch.
It is therefore a primary object of the present invention to provide an improved locating structure for silicon sheet of motor locator. The silicon sheet has a group of integrally projecting locating blocks radially opposite to each other. The base board is formed with locating holes respectively corresponding to the locating blocks. When a border of one pole section of the silicon sheet is aimed at the chip sensing point of the sensing switch, the locating blocks are inserted in the locating holes to truly locate the silicon sheet.
The present invention can be best understood through the following description and accompanying drawings wherein: